Lead titanate (PbTiO3) which has a perovskite structure (general formula ABO3) and is a ferroelectric material, shows piezoelectricity and is thus suitable for a piezoelectric material. It is difficult to form a strong ceramic (sintered body) having only a small number of pores and composed of lead titanate. Thus, dense piezoelectric ceramic compositions have been investigated and developed by partially substituting Pb and Ti by other elements and adding various components. The piezoelectric ceramic compositions are being practically applied to piezoelectric elements such as piezoelectric ceramic resonators.
For example, Patent Document 1 discloses a piezoelectric ceramic composition in which the PbO content is 42 to 48.5 mol %, TiO2 content is 43 to 52 mol %, the total molar amount of La2O3 and at least one of SrO, CaO, and BaO is 2.5 to 8 mol %, the MnO2 content of 0.1 to 2.0 mol %, and the proportion of at least one perovskite compound selected from Pb(Nb1/2Fe1/2)O3, Pb(Nb1/2Co1/2)O3, and Pb(Ni1/2Nb1/2)O3 is 3 mol % or less.
In Patent Document 1, the partial substitution of Pb in PbTiO3 by any one of Sr, Ca, and Ba and the partial substitution of Ti by Mn and a third component such as (Ni1/2Nb1/2) can eliminate defective dispersion occurring during production and expand the allowable range of production conditions, so that it is possible to stably supply the ceramic material with a uniform composition.
Patent Document 2 discloses a pyroelectric ceramic composition containing a main component composed of a compound having a composition represented by general formula (Pb1-xCax) [(Ni1/3Nb2/3)yTi1-y]O3 (wherein x and y satisfy 0.25≦x≦0.35 and 0.01≦y≦0.06) and containing 0.3 to 2.5 at % Mn as an auxiliary component.
In Patent Document 2, a pyroelectric ceramic composition with a Curie point Tc of 195° C. to 290° C. is provided by performing firing at a relatively low temperature of 1,100° C. to 1,200° C.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 63-182255 (claim 1; page (3), upper right column, line 5; and page (4), lower left column, lines 1 to in the same column on the same page)    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 1-261876 (claim 1; page (3), upper left column, lines 5 to 7 in the same column on the same page; and Table 1)